Opioids, also known as opioid agonists, are a group of drugs that exhibit opium or morphine-like properties. The opioids are employed primarily as moderate to strong analgesics, but have many other pharmacological effects as well, including drowsiness, respiratory depression, changes in mood and mental clouding without a resulting loss of consciousness. Opioids act as agonists, interacting with stereospecific and saturable binding sites in the brain and other tissues. Endogenous opioid-like peptides are present particularly in areas of the central nervous system that are presumed to be related to the perception of pain; to movement, mood and behavior, and to the regulation of neuroendocrinological functions. Opium contains more than twenty distinct alkaloids. Morphine, codeine and papaverine are included in this group.
By the middle of the nineteenth century, the use of pure alkaloids such as morphine rather than crude opium preparations began to spread throughout the medical world. Parenteral use of morphine tended to produce a more severe variety of compulsive drug use. The problem of addiction to opioids stimulated a search for potent analgesics that would be free of the potential to produce addiction. By 1967, researchers had concluded that the complex interactions among morphine-like drugs, antagonists, and what was then called xe2x80x9cmixed agonist-antagonistxe2x80x9d could best be explained by postulating the existence of more than one type of receptor for opioids and related drugs. With the advent of new totally synthetic entities with morphine-like actions, the term xe2x80x9copioidxe2x80x9d was generally retained as a generic designation for all exogenous substances that bind stereo-specifically to any of several subspecies of opioid receptors and produce agonist actions.
The potential for the development of tolerance and physical dependence with repeated opioid use is a characteristic feature of all the opioid drugs, and the possibility of developing psychological dependence (i.e., addiction) is one of the major concerns in the use of the treatment of pain with opioids, even though iatrogenic addiction is rare. Another major concern associated with the use of opioids is the diversion of these drugs from the patient in pain to another (non-patient) for recreational purposes, e.g., to an addict.
The overall abuse potential of an opioid is not established by any one single factor. Instead, there is a composite of factors, including, the capacity of the drug to produce the kind of physical dependence in which drug withdrawal causes sufficient distress to bring about drug-seeking behavior; the ability to suppress withdrawal symptoms caused by withdrawal from other agents; the degree to which it induces euphoria similar to that produced by morphine and other opioids; the patterns of toxicity that occur when the drug is dosed above its normal therapeutic range; and physical characteristics of the drugs such as water solubility. Such physical characteristics may determine whether the drug is likely to be abused by the parenteral route.
In the United States, the effort to control the compulsive drug user includes efforts to control drug availability by placing restrictions on the use of opioids in the treatment of pain of compulsive drug users. In practice, the physician is often faced with a choice of administering potent opioid analgesics even to persons who seem predisposed to develop psychological dependence, i.e., addiction, on such drugs. In view of this problem, it has been recommended that these patients should not be given an opioid when another drug without a potential for abuse will suffice; and further that these patients should not be permitted to self-administer such drugs parenterally and should only be given a few days"" supply at a time.
At least three basic patterns of opioid use and dependence have been identified. The first involves individuals whose drug use begins in the context of medical treatment and who obtain their initial supplies through, e.g., physicians. Another pattern begins with experimental or xe2x80x9crecreationalxe2x80x9d drug use and progresses to more intensive use. A third pattern involves users who begin in one or another of the preceding ways but later switch to oral opioids such as methadone, obtained from organized addiction treatment programs.
Tolerance refers to the need to increase the dose of opioid over a period of time in order to achieve the same level of analgesia or euphoria, or the observation that repeated administration of the same dose results in decreased analgesia, euphoria, or other opioid effects. It has been found that a remarkable degree of tolerance develops to the respiratory depressant, analgesic, sedative, emetic and euphorigenic effects of opioids. However, the rate at which this tolerance may develop in either an addict or in a patient requiring treatment of pain, depends on the pattern of use. If the opioid is used frequently, it may be necessary to increase the dose. Tolerance does not develop equally or at the same rate to all the effects of opioids, and even users who are highly tolerant to respiratory depressant effects continue to exhibit miosis and constipation. Tolerance to opioids largely disappears when the withdrawal syndrome has been completed.
Physical dependence may develop upon repeated administrations or extended use of opioids. Physical dependence is gradually manifested after stopping opioid use or is precipitously manifested (e.g., within 20 minutes) after administration of a narcotic antagonist (referred to xe2x80x9cprecipitated withdrawalxe2x80x9d). Depending upon the drug to which dependence has been established and the duration of use and dose, symptoms of withdrawal vary in number and kind, duration and severity. The most common symptoms of the withdrawal syndrome include anorexia, weight loss, pupillary dilation, chills alternating with excessive sweating, abdominal cramps, nausea, vomiting, muscle spasms, hyperirritability, lachrymation, rinorrhea, goose flesh and increased heart rate. Abstinence syndrome typically begins to occur 24-48 hours after the last dose, and the syndrome reaches its maximum intensity about the third day and may not begin to decrease until the third week.
Psychological dependence (i.e., addiction) on opioids is characterized by drug-seeking behavior directed toward achieving euphoria and escape from, e.g., psychosociocconomic pressures. An addict will continue to administer opioids for non-medicinal purposes and in the face of self-harm.
Pharmacologically, opioid antagonists typically block or reverse all of the effect of opioid agonists. One use of opioid antagonists is as a once-a-day treatment of naltrexone to block euphoric effects that might be otherwise obtained upon administration of opioids to addicts. Small doses of opioid antagonists have been used to determine whether individuals are physically dependent on opioids. Most commonly, opioid antagonists are used to reverse the effects of opioids on individuals who have overdosed on opioid agonist drugs.
There have previously been attempts in the art to control the abuse potential associated with opioid analgesics. Typically, a particular dose of an opioid analgesic is more potent when administered parenterally as compared to the same dose administered orally. Therefore, one popular mode of abuse of oral medications involves the extraction of the opioid from the dosage form, and the subsequent injection of the opioid (using any xe2x80x9csuitablexe2x80x9d vehicle for injection) in order to achieve a xe2x80x9chigh.xe2x80x9d Attempts to curtail abuse have therefore typically centered around the inclusion in the oral dosage form of an opioid antagonist which is not orally active but which will substantially block the analgesic effects of the opioid if one attempts to dissolve the opioid and administer it parenterally.
For example, the combination of pentazocine and naloxone has been utilized in tablets available in the United States, commercially available as Talwin(copyright)Nx from Sanofi-Winthrop. Talwin(copyright)Nx contains pentazocine hydrochloride equivalent to 50 mg base and naloxone hydrochloride equivalent to 0.5 mg base. Talwin(copyright)Nx is indicated for the relief of moderate to severe pain. The amount of naloxone present in this combination has no action when taken orally, and will not interfere with the pharmacologic action of pentazocine. However, this amount of naloxone given by injection has profound antagonistic action to narcotic analgesics. Thus, the inclusion of naloxone is intended to curb a form of misuse of oral pentazocine which occurs when the dosage form is solubilized and injected. Therefore, this dosage has lower potential for parenteral misuse than previous oral pentazocine formulations. However, it is still subject to patient misuse and abuse by the oral route, for example, by the patient taking multiple doses at once.
Sunshine, et al. xe2x80x9cAnalgesic Efficacy of Pentazocine Versus a Pentazocine-Naloxone Combination Following Oral Administrationxe2x80x9d, Clin. J. Pain, 1988:4:35-40, reported on the effect of the addition of 0.5 mg naloxone on the analgesic efficacy of pentazocine 50 mg. The combination was found to be significantly less efficacious than pentazocine for the sum of the pain intensity difference (SPID), and for relief and pain intensity difference (PID) at the fourth hour. For patients with moderate baseline pain, the combination produced significantly less pain relief than pentazocine for SPID and for relief and PID at hours 3 and 4. In patients with severe baseline pain, there was no significant difference found between pentazocine and the combination of pentazocine plus naloxone.
Wang, et al. xe2x80x9cCrossover and Parallel Study of Oral Analgesicsxe2x80x9d, J. Clin Pharmacol 1981; 21:162-8, studied the combination of naloxone 0.25 mg and Percodan(copyright) (composed of 4.5 mg oxycodone HCl, oxycodone terephthalate 0.28 mg, aspirin 224 mg, phenacetin 160 mg, and caffeine 32 mg) compared to Percodan(copyright) alone, and placebo in a crossover study of patients with chronic pain. The combination had lower mean scores than Percodan(copyright) alone for most of the analgesic hourly parameters in the later hours of the trial. However, for the summary variables, the combination showed no significant difference from either placebo or Percodan(copyright).
A fixed combination of buprenorphine and naloxone was introduced in 1991 in New Zealand (Temgesic(copyright)Nx, Reckitt and Colman) for the treatment of pain.
A fixed combination therapy comprising tilidine (50 mg) and naloxone (4 mg) has been available in Germany for the management of severe pain since 1978 (Valoron(copyright)N, Goedecke). The rationale for the combination of these drugs is effective pain relief and the prevention of tilidine addiction through naloxone-induced antagonisms at the morphine receptor.
U.S. Pat. No. 3,773,955 (Pachter, et al.) described orally effective analgetic compositions which upon parenteral administration do not produce analgesia, euphoria, or physical dependence, and thereby prevent parenteral abuse of the analgetic agents. Such compositions contained from about 0.1 mg to about 10 mg naloxone per analgetic oral dose. This reference was not concerned with oral abuse of opioids.
U.S. Pat. No. 3,493,657 (Lewenstein, et al.) described compositions comprising naloxone and morphine or oxymorphone, which compositions were said to provide a strong analgesic effect without the occurrence of undesired side effects such as hallucinations.
U.S. Pat. No. 4,457,933 (Gordon, et al.) described a method for decreasing both the oral and parenteral abuse potential of strong analgetic agents such as oxycodone, propoxyphene and pentazocine, by combining an analgesic dose of the opioid with naloxone in a specific, relatively narrow range. Oxycodone-naloxone compositions having a ratio of 2.5-5:1 parts by weight and pentazocine-naloxone compositions having a ratio of 16-50:1 parts by weight were preferred. The dose of naloxone which was to be combined with the opioid is stated to substantially eliminate the possibility of either oral or parenteral abuse of the opioid without substantially affecting the oral analgesic activity thereof.
U.S. Pat. No. 4,582,835 (Lewis) describes a method of treating pain by administering a sublingually effective dose of buprenorphine with naloxone. Lewis describes dosage ratios of naloxone to buprenorphine from 1:3 to 1:1 for parenteral administration, and from 1:2 to 2:1 for sublingual administration.
It has been increasingly recognized in the art that oral opioid formulations are not only being abused by the parenteral route, but also via the oral route when the patient or addict orally self-administers more than the prescribed oral dose during any dosage interval. There is therefore a need for the development of a formulation for the treatment of pain which is administrable orally and which provides a lower potential for oral abuse.
To the inventors"" knowledge, a ratio of opioid agonist to opioid antagonist which would be analgesically effective when the combination is administered orally, but which is aversive in a physically dependent subject has not been recognized to date.
It is an object of the invention to provide an oral dosage form of an opioid analgesic which is subject to less abuse potential via the oral route than prior commercially available dosage forms.
It is a further object of the present invention to provide an oral dosage form of an opioid analgesic and method which provides therapeutic analgesia and which also provides a negative, xe2x80x9caversivexe2x80x9d experience when a large amount of the opioid, e.g., about 2-3 times the usually prescribed dose, is taken by or administered to a physically dependent subject.
It is a further object of the present invention to provide an oral dosage form of an opioid analgesic and a method for providing therapeutic analgesia in a manner which is not as positively reinforcing in non-physically dependent subjects taking more than the usually prescribed dose, e.g., about 2-3 times the usually prescribed dose of the opioid, as compared to the same amount of opioid without the antagonist.
It is a further object of the invention to provide a method of treating pain in human patients with an oral dosage form of an opioid analgesic while reducing the oral abuse potential of dosage form.
It is a further object of the invention to provide a method of manufacturing an oral dosage form of an opioid analgesic such that it has less oral abuse potential.
The above objects and others are achieved by the present invention, which is directed in part to the surprising finding that there exists a ratio of opioid antagonist to opioid agonist (analgesic) which is analgesically effective when the combination is administered orally, but which is aversive in a physically dependent subject. To the inventor""s knowledge, this was not even considered by those skilled in the art, e.g., an addictionologist, analgesiologist, a clinical pharmacologist. It is surprising that one combination product (of combined antagonist/agonist) could in essence be therapeutic to one population (patients in pain), while being unacceptable (aversive) in a different population (e.g., physically, dependent subjects) when administered at the same dose or at a higher dose than the usually prescribed dosage, e.g., about 2-3 times the usually prescribed dose of the opioid.
The present invention is directed in part to an oral dosage form comprising an orally analgesically effective amount of an opioid agonist and an opioid antagonist in a ratio which maintains analgesic efficacy by the opioid analgesic but which may decrease analgesia somewhat as assessed by direct measurement in patients or by the use of one or more surrogate measures of opioid efficacy (analgesia) in human subjects. Surrogate measures of opioid efficacy (analgesia) include sedation, respiratory rate and/or pupil size (via pupillometry), and visual analogue scale (xe2x80x9cVASxe2x80x9d) for xe2x80x9cdrug effectxe2x80x9d. Such surrogate measures are affected in a direction which indicates reduced opioid effect, as compared to the same dose of opioid without the concommitant dose of opioid antagonist.
In certain preferred embodiments where the opioid is hydrocodone and the antagonist is naltrexone, the oral dosage form includes hydrocodone in the form of its bitartrate salt and naltrexone in the form of its hydrochloride salt.
In certain preferred embodiments where the opioid is hydrocodone and the antagonist is naltrexone, the ratio of naltrexone to hydrocodone is preferably from about 0.03-0.27:1 by weight, and more preferably from about 0.05-0.20:1 by weight.
The present invention is directed to a method of preventing oral abuse of an oral opioid formulation by a subject, comprising preparing an oral dosage form which comprises an orally analgesically effective amount of an opioid agonist and an opioid antagonist in a ratio which maintains analgesic efficacy by the opioid analgesic but which may decrease analgesia somewhat as assessed by direct measurement in patients or by the use of one or more surrogate measures of opioid effect in human subjects. When the oral dosage form is taken by a physically dependent subject at a relatively large dosage, e.g., about 2-3 times the usually prescribed dose, that use is aversive in a physically dependent human subject and preferably not as positively reinforcing as the opioid (ingested alone) in a non-physically dependent human subject.
The present invention is also directed to a method of treatment, comprising orally administering an orally analgesically effective amount of an opioid agonist together with an opioid antagonist in a ratio which maintains analgesic efficacy by the opioid analgesic but which may decrease analgesia somewhat by direct measurement in patients or by the use of one or more surrogate measures of opioid effect in human subjects.
The present invention is further directed in part to oral dosage forms comprising a combination of an orally analgesically effective amount of an opioid agonist and an orally active opioid antagonist, the opioid antagonist being included in an amount (i) which does not cause a reduction in the level of analgesia elicited from the dosage form upon oral administration to a non-therapeutic level and (ii) which provides at least a mildly negative, xe2x80x9caversivexe2x80x9d experience in physically dependent subjects (e.g., precipitated abstinence syndrome) when the subjects attempt to take at least twice the usually prescribed dose at a time (and often 2-3 times that dose or more), as compared to a comparable dose of the opioid without the opioid antagonist present. Preferably, the amount of naltrexone included in the oral dosage form is less positively reinforcing (e.g., less xe2x80x9clikedxe2x80x9d) to a non-physically dependent opioid addict than a comparable oral dosage form without the antagonist included. Preferably, the formulation provides effective analgesia when orally administered.
For purposes of the present invention, the phrase xe2x80x9cwhich may decrease analgesia somewhat as assessed by direct measurement in patients or by the use of one or more surrogate measures of opioid analgesic efficacy in human subjectsxe2x80x9d means that the patient in pain may or may not appreciably notice the difference between the formulation administered in accordance with the invention (i.e., combination of opioid agonist/antagonist) and a similar formulation which includes the same dose of opioid agonist without the opioid antagonist, but will obtain an analgesic effect from the combination. The pharmacodynamic effect (analgesia) of the formulations administered in accordance with the invention can be described by means of, for example, scores from an analgesic questionnaire reported by the patients at serial times following administration of the dosage form. Summary measures of analgesia include the sum of pain intensity difference (SPID) and total pain relief (TOTPAR).
In certain preferred embodiments, the amount of opioid antagonist included in the dosage form may cause a clinically significant reduction in the level of analgesia elicited from the dosage form upon oral administration, e.g., as measured by surrogate measures such as a Visual Analogue Scale (xe2x80x9cVASxe2x80x9d) for xe2x80x9cdrug effectxe2x80x9d. In other embodiments, the amount of opioid antagonist included in the oral dosage form may cause a noticeable reduction in the level of analgesia elicted from the dosage form upon oral administration, but does not reduce the level of analgesia provided to a subtherapeutic level.
Preferably, the amount of antagonist included in the oral dosage form is less positively reinforcing (e.g., less xe2x80x9clikedxe2x80x9d) by a non-physically dependent opioid subject than a comparable oral dosage form without the antagonist included.
The present invention is also directed to a method of preparing an oral dosage form of an opioid analgesic intended for the treatment of pain in human patients in a manner which minimizes the likelihood of oral abuse of the dosage form, combining an orally analgesically effective amount of an opioid agonist together with an opioid antagonist in a ratio which maintains analgesic efficacy by the opioid analgesic but which may decrease analgesia somewhat by direct measurement in patients or by the use of one or more surrogate measures of analgesia in human subjects. In certain embodiments, the combination when orally administered provides a clinically significant reduction in the level of analgesia elicited from the dosage form upon oral administration (as compared to the same dose of opioid alone), and provides at least a mildly negative, xe2x80x9caversivexe2x80x9d experience in a physically dependent subject (e.g., precipitated abstinence syndrome) when the subject takes more than the usually prescribed or usual dose of opioid. The subject may be, for example, an addict who attempts to achieve euphoria (a xe2x80x9chighxe2x80x9d) by taking more than (e.g., at least 2-3 times) the usually prescribed dose at a time. The amount of opioid antagonist included in the dosage form may or may not cause a noticeable reduction in the level of analgesia elicited from the dosage form upon oral administration, e.g., as measured by pharmacodynamic parameters such as a Visual Analogue Scale (xe2x80x9cVASxe2x80x9d) for drug effect, but preferably allows the dosage form to nevertheless provide effective analgesia. In certain preferred embodiments of the method, the dose of opioid antagonist appreciably affects a surrogate measure of opioid analgesic effect. In certain preferred embodiments, the amount of antagonist included in the oral dosage form is less positively reinforcing (e.g., less xe2x80x9clikedxe2x80x9d) by a non-physically dependent subject than a comparable oral dosage form without the antagonist included.
The oral pharmaceutical compositions containing the inventive combination of drugs set forth herein may be in the form of tablets, liquids, troches, lozenges, aqueous or oily suspensions, multiparticulate formulations including dispersable powders, granules, matrix spheroids or coated inert beads, emulsions, hard or soft capsules or syrups or elixirs, microparticles (e.g., microcapsules, microspheres and the like), buccal tablets, etc. The dosage forms of the present invention may include any desired pharmaceutically acceptable excipients known to those skilled in the art. The dosage forms may further provide an immediate release of the opioid agonist and the opioid antagonist. In certain preferred embodiments, the dosage forms provide a sustained release of the opioid agonist, and provide the part or all of the dose of opioid antagonist in (i) immediate release form, (ii) sustained release form, or (iii) both immediate and sustained release form. Such embodiments may further comprise a portion of the opioid agonist in immediate release form. Sustained release may be accomplished in accordance with formulations/methods of manufacture known to those skilled in the art of pharmaceutical formulation, e.g., via the incorporation of a sustained release carrier into a matrix containing the opioid agonist and opioid antagonist; or via a sustained release coating of a matrix containing the opioid agonist and opioid antagonist.
The invention may provide for a safer product (eg, less respiratory depression) as well as one with a slower rate of opioid tolerance and physical dependency development.
In certain other preferred embodiments, the opioid included in the dosage form is a different orally active opioid agonist than hydrocodone. The ratio of naltrexone included in such formulations can be readily determined based on a simple calculation, taking into account the known equianalgesic dosages of various opioid analgesics as compared to hydrocodone. Equianalgesic dosages of various opioid analgesics are provided below, and are otherwise known to those skilled in the art, e.g, from Foley, K. xe2x80x9cThe Treatment of Cancer Pain;xe2x80x9d N. Engl. J Med. 1985;313:84-95, hereby incorporated by reference. In yet further aspects of this embodiment, a different opioid antagonist is substituted for naltrexone, using equiantagonistic doses thereof.
In certain embodiments, a combination of two opioid analgesics is included in the formulation. In further embodiments, one or more opioid analgesics is included and a further non-opioid drug is also included, in addition to the opioid antagonist. Such non-opioid drugs would preferably provide additional analgesia, and include, for example, aspirin, acetaminophen, non-steroidal antiinflammatory drugs (xe2x80x9cNSAIDSxe2x80x9d), NMDA antagonists, and cycooxygenase-II inhibitors (xe2x80x9cCOX-II inhibitorsxe2x80x9d). In yet further embodiments, a non-opioid drug can be included which provides a desired effect other than analgesia, e.g., antitussive, expectorant, decongestant, or antihistamine drugs, and the like.
The term xe2x80x9cparenterallyxe2x80x9d as used herein includes subcutaneous injections, intravenous, intramuscular, intrasternal injection or infusion techniques.
The term xe2x80x9ceffective analgesiaxe2x80x9d is defined for purposes of the present invention as a satisfactory reduction in or elimination of pain, along with a tolerable level of side effects, as determined by the human patient.
The term xe2x80x9csustained releasexe2x80x9d is defined for purposes of the present invention as the release of the drug (opioid analgesic) from the oral formulation at such a rate that blood (e.g., plasma) concentrations (levels) are maintained within the therapeutic range (above the minimum effective analgesic concentration or xe2x80x9cMEACxe2x80x9d) but below toxic levels over a period of time indicative of a twice-a-day or a once-a-day formulation.
The term xe2x80x9csteady statexe2x80x9d refers to a time when the rate of elimination of a drug is the same as the rate of absorption of that drug into the body.
For purposes of the present invention, the term xe2x80x9copioid agonistxe2x80x9d is interchangeable with the term xe2x80x9copioidxe2x80x9d or xe2x80x9copioid analgesicxe2x80x9d and shall include the base of the opioid, mixed agonist-antagonists, partial agonists, pharmaceutically acceptable salts thereof, stereoisomers thereof, ethers and esters thereof, and mixtures thereof.
For purposes of the present invention, the term xe2x80x9copioid antagonistxe2x80x9d shall include the base, pharmaceutically acceptable salts thereof, stereoisomers thereof, ethers and esters thereof, and mixtures thereof.